code: def _clear_screen():
      gl.glClear(gl.GL_COLOR_BUFFER_BIT)
      gl.glFinish()
  
file_path: vispy/vispy/gloo/gl/tests/test_functionality.py
imports: import sys
  import numpy
  from vispy.app import Canvas
  from vispy.testing import requires_application, requires_pyopengl, SkipTest, run_tests_if_main, assert_equal, assert_true
  from vispy.gloo import gl
  import pytest
label_desc: Use image node_id 6 for calling a global function with example usage: _clear_screen() without return types